Desk studies are most critical at the initial feasibility and planning phase of new road construction projects (Dumbleton & West 1974). Decisions made at this early stage on the selection of alignment and the approach to design and construction are critical to scheme costs and to the future stability and operation of a road. While the advent of satellite imagery and geographical information systems (GIS) technology in particular (Section B2.7) has meant that desk studies have become potentially far more wide-ranging than they were even 10 years ago, the traditional desk study still remains valid and important, and often provides the bulk of information.
The traditional desk study essentially combines data sources that are conventionally available in paper format, namely topographical maps, geological maps and aerial photographs (although digital maps and orthorectified photographs are now much more common place). Table B2.1 lists typical information that can be obtained from these three principal data sources, though their availability varies significantly (Hearn 2004). Topographical and geological maps are normally available through government agencies and usually small-scale mapping can be downloaded from the internet prior to embarking on field investigations, either under license or for a fee. Unfortunately, published geological maps in many countries are small scale and show Formation-level (stratigraphic age) information only; the distribution of rock types, information that is most relevant to engineering, is often not shown. Even where larger scale geological mapping is available it usually pays ‘very little attention to surface formations.
Figures & Tables
This book provides a complete guide to the study, design, construction and management of landslide and slope engineering measures for mountain roads, with an emphasis on low-cost. The geographical focus of the book is on the tropics and sub-tropics, but is also highly relevant to other regions where heavy rain, steep slopes and weak soils and rocks combine to create slope instability. The causes and mechanisms of landslides are described, and the hazards they pose to mountain roads are illustrated. Methods of desk study, field mapping and ground investigation are reviewed and illustrated, with an emphasis on geomorphological and engineering geological techniques. The design and construction of alignments, earthworks, drainage, retaining structures, the stabilization of soil slopes and rock slopes, and the control of erosion on slopes and in rivers and streams are covered. Slope management as part of road maintenance and operation is reviewed, and procedures for risk assessment and works prioritization are described.